Cisco CCNA - CCENT Certification Exam Training - Broadcasts, Hubs, Routers, And Switches

In a previous Cisco CCENT certification exam tutorial, we talked about broadcasts and the potential of a broadcast storm. (If you missed that one, visit my website's Tutorials section.) In today's tutorial, we'll discuss several different common network devices and how they help to limit broadcast propagation - or in some cases, how they do not help!

In the "do not help" department, we'll find hubs and repeaters. These two devices operate at Layer 1 of the OSI model (the Physical layer), and their sole purpose is to strengthen the electrical signals sent over the cable. They don't have anything to do with switching or routing, and they do not help to limit broadcasts. (A hub is basically just a repeater with more ports.)

On the other end of the spectrum, we have routers. Routers operate at Layer 3 of the OSI model (the Network layer), and by default routers do not forward broadcasts. They can be configured to "translate" certain broadcast types into unicasts, but you'll learn more about that in your CCNA studies.

Since routers do not forward broadcasts, there's a misconception that routers have nothing to do with broadcasts. Routers can indeed generate broadcasts, and they can accept them - but they will not forward them. That's an important distinction.

Between these two extremes, we find switches. Switches operate at Layer 2 of the OSI model (the Data Link layer), and the default behavior of a switch is to accept a broadcast and forward it out every other single port on that switch except the port that first received the broadcast.

If that sounds like a lot of broadcast forwarding, it is! If we have an 80-port switch and one port receives a broadcast, by default a copy of that broadcast is going to be forwarded out the other 79 ports. Most likely, not all of those hosts connected to those switchports need to see that broadcast, and sending unnecessary broadcast results in an unnecessary use of network resources, particularly bandwidth.

Luckily for us, there is a way to configure a Cisco switch to limit which ports receive that broadcast, and we'll take a look at that method in the next installment of my Cisco CCENT certification exam tutorial series!

CompTia A+ Training - Looking at Networks

Knowing about networks is vital to a role as computer technician. In the A+ certification, module six you explore what networks are and how they work through a series of knowledge and practical based questions, enabling you to handle the practical and theoretical side of I.T.

For starters, module 6 of the A+ certification explores what exactly a network is. A network is a collection of computers or devices that are connected together in order to cross communicate with one another. It allows various users to exchange information between one another from one computer to another. They are various network types, including WANS (wide area network), LANS (local area network), HANS (home area network), PANS (personal area network) and the intranet (a set of networks using internet protocol) etc. There are various methods to connect as well, including wired and wireless methods, which can connect up as little as two devices up to hundreds.

You will also need to know the hardware required for a network. Some basic structural components do remain the same on any network, whilst other hardware components vary from network type to network type. Here's a few of the hardware components, you will need to get acquainted with as an I.T technician.

Network Interface Cards: Or NICs as they are also known. NICS, network adapters or network cards are a type of hardware that allows computers to communicate over a computer network. Without this connection medium, you would not be able to access the computer network through your computer.

Hubs: You've probably come across one of these at some point. The hub (Ethernet hub, active hub, network hub etc) is simply a device that connects multiple Twisted Pair (the copper wire for Ethernet) or fiber optic Ethernet devices together. Once data is received to one port, it is passed on to the other ports without regulation.

Repeaters: Let's say there's an obstruction in your networks way - well a Repeater is the device used to solve this problem. by receiving and strengthening a signal (analogue and digital) and then retransmitting it, the signal can reach further, as well as overcome any obstacles in its path.

Network Bridges: Similar to Repeaters and Hubs, but ever so slightly different as a Network Bridge not only connects at the physical level of the OSI model (Open Systems Interconnection model), but the second layer too. This first level, without the overlay of computer jargon, specifies the relationship between the transmission medium (i.e. copper wires, fiber optics) and device, whilst layer two is the data link layer which allows transference of data between network entities and corrects any mishaps in the first layer.

A Network Bridge is far more complex than a hub, as it makes connections between the port and network address, allowing traffic to reach that port only. A hub instead relays all the data to all the ports, often causing collisions and slowing down traffic. A Network Bridge, unlike the Hub which does not recognise the data source, where it is going and what the data means, instead manages the data before it decides to send it to another network segment.